1. Field of the Invention
The present invention relates to a scroll compressor, and more particularly, to an apparatus for varying the capacity in a scroll compressor capable of minimizing power consumption by widening a range of varying the capacity of the compressor.
2. Description of the Background Art
In general, a compressor converts electric energy into kinetic energy, and compresses a refrigerant by the kinetic energy. The compressor is the kernel of a freezing cycle system, and according to compression mechanisms, there are various kinds of compressors such as a rotary compressor, a scroll compressor, a reciprocating compressor and the like. The freezing cycle system including such a compressor is used in a refrigerator, a showcase or the like.
In general, a scroll compressor continuously sucks, compresses and discharges a gas as an orbiting scroll orbits in meshing engagement with a fixed scroll upon receiving a driving force of a driving motor. The orbiting scroll and the fixed scroll are provided with wraps having an involute shape, respectively. A plurality of compression pockets are formed by the wrap of the fixed scroll and the wrap of the orbiting scroll. According to the orbiting movement of the orbiting scroll, while the compression pockets move towards a discharge hole through which the gas is discharged and are gradually contracted in volume, thereby compressing a gas.
In general, one pair of compression pockets, each of which is symmetrical about a discharge port, are formed. Two compression pockets as one pair have an identical volume. When one pair of compression pockets move towards a discharge hole as gas is sucked at the suction side, another pair of compression pockets following one pair of compression pockets are formed at the suction side. Such processes are repeatedly performed.
Meanwhile, an asymmetrical scroll compressor in which a volume of one compressor out of one pair of compression pockets is relatively large has been developed as a structure by which a volume to be compressed by the compression pockets can be increased.
In the scroll compressor, a rotary force generated from the driving motor is transmitted to the orbiting scroll as follows. An eccentric portion of a rotary shaft coupled to the driving motor is inserted into a boss portion formed at a lower portion of a circular plate of the orbiting scroll, and the rotary force is transmitted to the boss portion of the orbiting scroll through the eccentric portion of the rotary shaft. However, in case there are big changes in volumes in the compression pockets formed by the wrap of the fixed scroll and the wrap of the orbiting scroll, such a structure makes the orbiting movement of the orbiting scroll unstable because the compression pockets for compressing a gas is at a certain distance from the boss portion and the eccentric portion to which the rotary force of the driving force is transmitted.
In addition, as shown in FIGS. 1 and 2, as a structure for increasing the compression volume of the scroll compressor, a wrap 12 having a certain height is formed on a circular plate 11 of an orbiting scroll 10, and a wrap filling portion 13 having a certain height is formed at the wrap 12 side at the center of the circular plate 11. The wrap filling portion 13 is formed with a certain height to be positioned inside the wrap 12 from an inner end of the wrap 12 to a portion at which the wrap 12 is extended by a 360 angle. In addition, an insertion groove 14 into which an eccentric portion 21 of a rotary shaft 20 is inserted is formed at a lower surface of the circular plate 11, and the insertion groove 14 is formed to the inner side of the wrap filling portion 13. And, the eccentric portion 21 of the rotary shaft is inserted into the insertion groove 14. A section of the wrap filling portion 13 has such a shape that the eccentric portion 21 of the rotary shaft can be inserted into.
In such a structure, the eccentric portion 21 of the rotary shaft is positioned to the inner side of the wrap filling portion 13 of the orbiting scroll. Accordingly, as a position at which compression pockets (P) formed by the wrap 12 of a fixed scroll 30 in meshing engagement with the orbiting scroll 10 and the wrap 12 of the orbiting scroll overlaps with a position of the eccentric portion 21 to which a rotary force is transmitted, the structure allows the stable orbiting movement of the orbiting scroll 10 on condition that compression ratio is high. Moreover, since the wrap filling portion 13 is formed at the center of the orbiting scroll wrap 12, a volume of the discharge side is reduced, thereby relatively increasing the compression ratio of the gas to be discharged. Such a technique is proposed in JP2000-329079.
Meanwhile, in case of an airconditioner using a freezing cycle system provided with a compressor, varying the capacity of the compressor is required to reduce power consumption of the airconditioner according to a change of seasons: spring, summer, autumn and winter.
The mechanisms for varying the capacity of the compressor includes a method for controlling the number of the rotation of the driving motor constituting the compressor, a method for bypassing or leaking a gas, and a method of mixing the two.
The method for controlling the number of the rotation of the driving motor has a wide range of varying the capacity and the excellent performance, but manufacturing unit cost is high. Also, an additional device is required to settle the oil supply problem by the small rotation number, and reliability on a rubbing portion needs to be secured by the great rotation number.
The method for bypassing a gas can reduce manufacturing unit cost, but has a narrow range of varying the capacity and the low performance.